The term radiosurgery refers to a procedure in which intense and precisely directed doses of radiation are delivered to a target region in a patient, in order to destroy tumorous cells or otherwise treat the target region. The term radiotherapy refers to a procedure in which radiation is applied to a target region for therapeutic, rather than necrotic, purposes. The amount of radiation utilized in radiotherapy is typically about an order of magnitude smaller, as compared to the amount used in radiosurgery. Radiotherapy is frequently used to treat early stage, curable cancers. For convenience, the term “radiosurgery” in this application shall henceforth mean “radiosurgery and/or radiotherapy.”
In radiosurgery, it is necessary to determine with precision the location of the target region (and surrounding critical structures) relative to the reference frame of the treatment device. It is also necessary to control the position of the radiation source so that its beam can be precisely directed to the target tissue while avoiding surrounding healthy tissue, with control of propagation in and through other body structures.
To effect such beam position control, a frameless stereotactic radiosurgery system has been developed, which implements image-guided radiosurgery using a robot. An image-guided robotic system provides the requisite beam position control for accurate delivery of therapeutic radiation, while eliminating the need for rigid stereotactic frames. Such image-guided robotic systems typically include a treatment beam generator, for example an x-ray source, mounted onto a robot, and a controller. The x-ray source provides precisely shaped and timed radiation beams. Using pre-treatment scan data, as well as treatment planning and delivery software, the controller acquires information regarding the pre-treatment position and orientation of the treatment target region. The patient is usually placed on a support device, such as a couch or a table. During treatment, an imaging system repeatedly measures the position and orientation of the target relative to the x-ray source. Prior to the delivery of radiation at each delivery site, the controller directs the robot to adjust the position and orientation of the x-ray source, in accordance with the measurements made by imaging system, so that the requisite dose of the treatment beam can be applied to the treatment target within the patient.
While operating these image-guided robotic systems, it is necessary to adjust the position and orientation of the patient in order to ensure that the target within the patient remains properly aligned with respect to the treatment beam. The position and orientation of the patient must be corrected, for example, in order to compensate for any motion (such as respiratory motion, sneezing, or shifting) that the patient may undergo during treatment.
Accordingly, it is desirable to provide a patient positioning assembly that includes a dynamic motion control mechanism for controlling the motion of the support device, so that the position and orientation of the support device can be adjusted as necessary.